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旱地生态系统碳氮过程对干旱响应与反馈的Meta分析

  • 郑雅晶1

    机 构：

    1. 1.南京农业大学 资源与环境科学学院/江苏省低碳农业与温室气体减排重点实验室,南京, 210095

    ×
  • ，邹建文1

    机 构：

    1. 1.南京农业大学 资源与环境科学学院/江苏省低碳农业与温室气体减排重点实验室,南京, 210095

    ×
  • ，刘树伟1

    机 构：

    1. 1.南京农业大学 资源与环境科学学院/江苏省低碳农业与温室气体减排重点实验室,南京, 210095

    ×

1.南京农业大学 资源与环境科学学院/江苏省低碳农业与温室气体减排重点实验室,南京, 210095；

A meta-analysis of response and feedback of terrestrial carbon and nitrogen cycling to drought

  • ZHENG Yajing1

    Affiliation：

    1. 1.College of Resources and Environmental Sciences/Jiangsu Key Laboratory of Low Carbon Agriculture and GHGs Mitigation,Nanjing Agricultural University,Nanjing 210095

    ×
  • ，ZOU Jianwen1

    Affiliation：

    1. 1.College of Resources and Environmental Sciences/Jiangsu Key Laboratory of Low Carbon Agriculture and GHGs Mitigation,Nanjing Agricultural University,Nanjing 210095

    ×
  • ，LIU Shuwei1

    Affiliation：

    1. 1.College of Resources and Environmental Sciences/Jiangsu Key Laboratory of Low Carbon Agriculture and GHGs Mitigation,Nanjing Agricultural University,Nanjing 210095

    ×

1.College of Resources and Environmental Sciences/Jiangsu Key Laboratory of Low Carbon Agriculture and GHGs Mitigation,Nanjing Agricultural University,Nanjing 210095；

作者简介:

郑雅晶,女,博士生,研究方向为陆地表层过程与全球变化.2019203052@njau.edu.cn;

刘树伟(通信作者),男,博士,教授,博士生导师,研究方向为农业温室气体减排途径与潜力.swliu@njau.edu.cn

中图分类号:S153;X71

文献标识码:A

DOI:10.13878/j.cnki.jnuist.2022.01.001

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目录contents

    摘要

    干旱会影响陆地生态系统碳氮循环,形成对气候变化的反馈效应.然而,目前国际上有关旱地生态系统碳氮过程对干旱的响应与反馈效应尚不清楚.本研究共收集整理了全球来自128篇文献的1344组原位观测数据进行Meta分析(Meta-analysis),用以定量评估旱地生态系统碳氮过程对干旱的响应程度和反馈效应.结果表明,干旱会显著降低植被碳库,且地上生物量碳对干旱的敏感性略高于地下生物量碳.土壤CO2和N2O排放在干旱条件下均显著减少.对于土壤碳氮库,干旱条件下,土壤有机碳库和氮库均无显著变化,相反,土壤可溶性有机碳库显著降低,土壤NO-3-N含量显著增加.此外,干旱还会导致净生态系统生产力(NEP)显著降低.本研究首次将干旱对土壤CO2和N2O排放的影响与植被和土壤碳氮库的变化联系起来,并得出以下结论:干旱虽会引起土壤碳排放减少,但由于其同时也会抑制植被的生长,导致在未来干旱的气候条件下,加剧旱地生态系统对气候变化的正反馈效应.

    Abstract

    Drought has been shown to alter terrestrial ecosystem carbon (C) and nitrogen (N) dynamics,and thus feedback to future climate.However,drought-induced changes in terrestrial upland C and N pools and the drought response of soil carbon dioxide (CO2) and nitrous oxide (N2O) fluxes are yet to be quantified.A meta-analysis was conducted that compiled 1344 measurements from 128 manipulative studies worldwide to obtain a general picture of terrestrial C and N cycling responses to soil drought stress and identify the primary driving factors.We showed that drought significantly decreased plant C pools,with stronger negative responses of aboveground than belowground C components.Drought significantly decreased soil CO2 and N2O fluxes.There were non-significant changes in soil organic C and N pools in response to drought;in contrast to a considerable decrease in soil dissolved organic C,there was a robust increase in soil NO-3-N following short-term drought impact.Furthermore,drought also significantly decreased Net Ecosystem Productivity (NEP).Our study provides insights into soil release of CO2 and N2O with a linkage to the changes in terrestrial C and N pools in response to drought across upland biomes.Our findings highlight that,despite the lowered soil C release rate,the capacity of upland biomes as a C sink to slow climate change would still be weakened in a future drier climate.

    关键词

    气候变化 ； 干旱 ； Meta分析 ； CO2 ； N2O ； 土壤碳库 ； 土壤氮库

  • 0 引言

  • 旱地土壤是大气中CO2和N2O的重要来源[1-2].相比于自然湿地和稻田,由于水分有效性低,旱地土壤更易因灌溉和降雨量减少而遭受干旱.降水格局改变可能会导致未来发生更多的干旱事件,进而对土壤碳氮循环产生潜在的不利影响[3].大量研究表明降水格局(包括降水持续时间和降水强度等)改变会对土壤CO2和N2O排放产生重要影响[4-6].气候模型预测,到2100年,地球上越来越多的地区将变得更加干旱,尤其是热带和亚热带地区[7-9].这种气候变化模式可能会改变土壤碳氮转化速率,进而影响植被和微生物对土壤碳氮底物的可利用性.除直接影响土壤碳氮底物的移动和扩散外,干旱还可以通过微生物固定和转化碳氮过程的水合作用间接对土壤养分循环产生影响[10-12].因此,从植被和土壤碳氮库的角度研究干旱如何影响土壤CO2和N2O排放,对于综合理解陆地生态系统碳氮循环对气候变化的响应十分重要[13].

  • 近年来,有大量研究探索土壤碳氮排放和土壤碳氮库对降水和灌溉减少的响应[4,6,14-16],但是不同研究所得出的结论不尽相同,这些不一致的结论(增加、减少和无影响)主要是包括气候、土地利用类型以及降雨频率和强度在内的多种环境控制因素综合作用的结果[15].因此,试图得出旱地土壤碳氮组分对干旱响应的一般性规律,有必要对全球范围内相关研究的试验数据进行整合分析.此外,从土壤碳氮库的变化了解干旱对土壤碳氮排放的影响有助于提高生物地球化学模型的预测能力.

  • 目前,国际上有关干旱对旱地土壤碳氮循环的影响程度及其对气候变化的反馈效应并不清楚.近年来,大量有关降水减少的Meta分析结果表明,土壤碳氮排放和植被生长在干旱条件下呈降低趋势,土壤矿质氮的有效性则呈增加趋势[2,13,17-18].这些整合分析研究并没有将土壤碳氮排放和生态系统碳库联系起来.因此,干旱条件下土壤CO2和N2O排放与生态系统碳库的相互作用程度是当前全球变化研究领域亟待解决的重要科学问题.

  • 本研究收集了全球有关干旱对旱地生态系统碳氮过程影响的1 344组原位观测数据,通过Meta分析定量评估了干旱对旱地土壤碳氮排放以及植被和土壤碳氮库的影响.此外,本研究还旨在探索影响土壤CO2和N2O排放对干旱响应的主要生物和非生物环境控制因子.本研究假设:1)干旱会减少土壤碳氮排放,降低植被和土壤碳库,进而改变生态系统碳平衡;2)土壤矿质氮有效性在干旱条件下表现为增加趋势,主要是因为植被和微生物对活性氮的吸收利用减少[2,19];3)干旱条件下,土壤碳库并不会因土壤CO2排放减少而呈增加趋势,主要原因是干旱会减少植被向土壤碳库的输入.此外,本研究预测旱地生态系统碳氮过程对干旱的响应还取决于干旱强度和试验的持续时间.

  • 1 方法

  • 1.1 数据的收集与纳入标准

  • 以“drought/rainfall reduction/precipitation reduction”、“soil”和“respiration/CO2/carbon dioxide/N2O/nitrous oxide”为关键词,不设时间限制(最后一次检索时间2018年7月21日),分别在Google Scholar、Web of Science和China National Knowledge Infrastructure(CNKI)等数据库中检索已发表干旱对旱地生态系统碳氮过程影响的相关论文,其中论文必须包含土壤CO2或N2O排放.同一篇论文中,除收集土壤CO2或N2O排放的数据外,若该论文同时也包含植被碳库和土壤碳氮库的数据,那么也需收集这一部分的数据.数据库中,干旱处理是通过使用挡雨棚或控制灌溉水量实现的,其减少的水分含量为对照的10%~100%(平均为72.83%);试验(包括间断和连续)持续时间的范围为0.20~13.00年.

  • 为避免发表偏倚,所收集的文献必须符合以下标准:1)为更好地理解试验干旱对旱地生态系统碳氮过程的影响,除野外田间试验外,盆栽试验也被考虑在内,室内培养试验被排除;2)各研究中试验区和对照区要处于同样的气候条件下;3)各研究必须包含干旱的处理方式(减少降水或灌溉)、干旱的强度和试验的持续时间;4)各指标的均值、样本量、方差或标准差均在文章中有说明或可通过软件Getdata从各研究的图表中进行提取或可通过计算得出;5)对于交互作用的研究,仅提取对照组和干旱组数据或同时包含其他气候变化因子的对照组和干旱组数据;6)研究中包含多个土壤深度的参数时,计算整个土壤剖面的平均值.按照以上标准,共收集到来自128篇文献的1 344组原位观测数据(图1),其中包括188组的土壤CO2和N2O排放同步观测数据.

  • 除土壤CO2和N2O排放、植被碳库和土壤碳氮库等关键的指标外,还需提取以下信息:文献背景信息(如作者、发表年份)、样本的重复数、试验方法和持续时间、干旱处理方式、干旱强度、施氮肥状况(施氮量和氮肥形式)、土地利用方式、采样点信息(如气候类型、年均温、年降雨量和经纬度)和土壤理化性质(如土壤碳氮含量、土壤温度、土壤pH和土壤水分含量).试验点的年均温和年降雨量在文章中没有说明时,根据其经纬坐标信息,通过全球气候数据库(http://www.worldclim.org/)直接进行查询获得.

  • 图1 109个原位观测点地理分布

  • Fig.1 Geographical distribution of 109in situ data measurements used in our analysis

  • 为进一步探讨不同因素对干旱引起旱地生态系统碳氮过程变化的影响,将数据分成不同的亚组,具体分组情况如下:

  • 1)按照干旱强度分为≤50%和＞50%;

  • 2)按照肥料效应分为施肥和不施肥;

  • 3)按照土地利用类型分为森林、草地和旱地农田;

  • 4)按照试验方法分为野外田间试验和盆栽试验;

  • 5)按照植被效应分为有植株参与和无植株参与;

  • 6)按照干旱处理方式分为减少降雨和减少灌溉;

  • 7)按照土壤质地分为砂土、壤土和黏土;按照土壤pH分为≤7和＞7;按照土壤有机碳质量分数分为≤1.7%和＞1.7%;

  • 8)按照土壤总氮质量分数分为≤0.08%和＞0.08%;

  • 9)按照土壤碳氮比分为≤10和＞10.

  • 1.2 数据处理与分析

  • 提取数据过程中,若文章提供的数据为标准误(SE),则需通过式(1)统一转换为标准差(SD):

  • SD=SE×n,
    (1)

  • 式中,n表示样本量.

  • Meta分析通过METAWIN 2.1软件(Sinauer Associates Inc.,Sunderland,MA,USA)实现,通过自然对数的响应比(ln R)作为效应值(effect size)来衡量干旱对旱地生态系统碳氮过程的影响,公式如下:

  • ln⁡R=ln⁡Xt/Xc,
    (2)

  • 式中,Xt和Xc分别表示试验组和对照组的均值.

  • 方差(v)为

  • v=St2ntXt2+Sc2ncXc2,
    (3)

  • 式中,St和Sc分别表示试验组和对照组的标准差,nt和nc分别表示试验组和对照组的样本量.

  • 利用非参数权重因子(w)对每项研究的效应值进行加权,权重因子(w)为方差(v)的倒数:

  • w=1v.
    (4)

  • 通过非参数权重加权后的效应值为ln R′:

  • ln⁡R'=ln⁡R×w.
    (5)

  • 加权后的平均效应值(RR++)计算公式为

  • RR++=∑k ln⁡RRk'∑k wk'
    (6)

  • 本研究采取随机效应模型进行Meta分析,当某一指标平均效应值95%置信区间和“0”没有交叉时,表示干旱对该指标有显著影响,即认为干旱对该指标的影响具有统计学意义,当效应值大于0时表示干旱对指标产生正效应,相反则表示产生负效应.本研究将总异质性Qt分为各亚组的组间异质性Qb和组内异质性Qw,通过组间异质性Qb来检验同一指标的效应值在不同亚组之间的差异.

  • 除Meta分析外,本研究还进行了单因素方差分析(ANOVA)、协方差分析(ANCOVA)、结构方程模型分析以及线性回归分析等.所有统计分析在JMP 7.0(SAS Institute CA,US,2007)、SPSS 13.0 (SPSS Inc.,Chicago,USA)以及R 3.5(R Development Core Team,2016)等软件中进行.

  • 2 结果

  • 2.1 干旱对植被生物量碳的影响

  • 总体而言,植被总生物量碳在干旱条件下明显降低(平均效应值=-0.23; 95%CI:-0.31~-0.15),且地上生物量碳(平均效应值=-0.22;95%CI:-0.29~-0.15)对干旱的敏感性略高于地下生物量碳(平均效应值=-0.19;95%CI:-0.29~-0.10).植被地上与地下生物量碳的比例(在干旱条件下虽有降低趋势,但并不显著(平均效应值=-0.05;95%CI:-0.17~0.06;图2a).

  • 2.2 干旱对土壤碳氮排放的影响

  • 总的来说,干旱会降低土壤CO2排放,其中土壤呼吸(平均效应值=-0.19;95%CI:-0.25~-0.14)和土壤异氧呼吸(平均效应值=-0.18;95%CI:-0.20~-0.15)均表现为显著降低(图2b).土壤异氧呼吸在不同的干旱强度、肥料效应、土地利用类型、试验方法、干旱处理方式、土壤pH和土壤碳氮比中对干旱的响应差异显著;而土壤呼吸仅在不同的土地利用类型和干旱处理方式中对干旱的响应差异显著(表1).此外,试验持续时间、土壤温度和土壤有机碳含量也会影响土壤CO2排放对干旱的响应(表2;图3).整体来看,与常规降水量或灌溉量相比,干旱会导致净生态系统生产力(NEP)显著降低(平均效应值=-0.37;95%CI:-0.53~-0.21;图2b).对于土壤氮排放,整合分析结果表明土壤N2O排放在干旱条件下显著减少(平均效应值=-0.29;95%CI:-0.44~-0.15;图2b),且不同的试验方法、植被效应、土壤质地、土壤pH和土壤总氮含量对其排放的影响差异显著(表1).

  • 图2 干旱对旱地生态系统碳氮过程的影响

  • Fig.2 The responses of carbon and nitrogen processes of upland ecosystems to drought

  • 表1 干旱对土壤呼吸、土壤异氧呼吸和土壤N2O排放影响因子的异质性分析

  • Table1 Between-group heterogeneity (Qb) for drought effect size among soil respiration, soil heterotrophic respiration and soil N2O emissions

  • 注:n为观测值个数;Q b表示组间异质性;加粗的数值代表差异显著.

  • 表2 干旱对土壤呼吸、土壤异氧呼吸和土壤N2O排放影响因子与环境和土壤因子的相关性分析

  • Table2 Correlations of the responses of soil respiration,soil heterotrophic respiration and soil N2O fluxes to drought against controlling factors

  • 注:n为观测值个数;corr.c.表示相关系数;加粗的数值代表差异显著.

  • 图3 干旱条件下环境和土壤因子影响土壤CO2排放的结构方程模型

  • Fig.3 Structural equation model describing the effects of environmental and soil factors on soil CO2 emission under drought

  • 2.3 干旱对土壤碳氮库的影响

  • 研究结果显示,干旱虽会导致土壤有机碳库呈降低趋势,但并不显著(平均效应值=-0.04;95%CI:-0.08~0.01;图2c).对土壤活性碳库组分而言,干旱会显著降低土壤可溶性有机碳库(平均效应值=-0.22;95%CI:-0.45~-0.06),但其对微生物生物量碳库的影响并不显著(平均效应值=-0.03;95%CI:-0.10~0.04;图2c).

  • 土壤总氮库在干旱条件下虽表现为增加趋势,但并不显著(平均效应值=0.004;95%CI:-0.04~0.04;图2d).对于土壤活性氮库,干旱对土壤矿质氮和铵态氮的有效性的影响均不显著(矿质氮,平均效应值=0.08;95%CI:-0.08~0.24;NH+4-N,平均效应值=-0.04;95%CI:-0.09~0.11),但会导致土壤硝态氮的有效性明显增加(平均效应值=0.26;95%CI:0.06~0.45),微生物生物量氮的有效性明显降低(平均效应值=-0.15;95%CI:-0.25~-0.05;图2d).此外,干旱对土壤碳氮比和微生物生物量碳氮比均无显著影响(土壤碳氮比,平均效应值=-0.02;95%CI:-0.07~0.03;微生物生物量碳氮比,平均效应值=0.02;95%CI:-0.08~0.11;图2e).

  • 3 讨论

  • 3.1 干旱对旱地生态系统碳氮库的影响

  • 本研究结果显示,植被和土壤有机碳库在干旱条件下均呈降低趋势,这主要是因为干旱会抑制植被生长和光合作用,不利于根系分泌物的产生与释放,导致土壤活性碳源供给减少,需要消耗土壤中固有的碳储存来维持土壤基本养分循环功能[2].其中,土壤有机碳库对干旱的响应不及植被碳库对干旱的响应明显,表明相比于土壤碳转化过程,植被生长和光合作用更易受到干旱的影响.Chen等[20]也认为总生态系统生产力(GEP)对土壤水分的敏感性要高于土壤碳组分,其原因可能是干旱会影响土壤微生物的活性,降低土壤养分的流动性和有效性[21-22].除抑制植被生长和光合作用外,干旱还会导致植被死亡[23].相对于植被地上部分碳而言,干旱会促进植被的光合产物向根系分配,提高地下部分的碳素固定,使植被容易从土壤中获取养分以满足干旱条件下其生存和生长的基本需求[24].因此,碳分配的这种变化可能会改变生态系统的碳平衡[13].

  • 本研究发现,土壤总氮含量在干旱条件下的增加效应并不显著.土壤硝态氮含量在干旱条件下的显著增加导致土壤矿质氮含量也呈增加趋势(图2d),这表明相比于其他氮循环过程,调节土壤矿质氮供给的微生物过程可能对干旱响应更敏感[17].此外,土壤硝态氮含量在干旱条件下表现为明显增加趋势,可能原因是相比于水分含量高的土壤,水分含量低的土壤中硝态氮的淋失和反硝化过程更不易发生.此外,Parker等[25]研究认为,地中海地区旱季的持续时间通常比其他地区长,在该地区观察到更高的土壤氮有效性主要是因为植被对氮吸收的减少.

  • Ren等[26]的Meta分析研究表明,土壤微生物生物量在降水减少条件下表现为明显降低趋势,这和本研究的整合分析结果一致.干旱会导致土壤微生物生物量减少,尤其是对生物量氮库的减少效应更明显,主要是因为水分减少会降低溶质的扩散率,限制微生物对养分的获取,进而抑制其生长[27-30].此外,干旱状况(持续时间或强度)会影响微生物对水分的敏感性,进而通过改变旱地土壤微生物群落多样性及结构组成来影响它们的生长.

  • 3.2 干旱对旱地生态系统碳氮排放的影响

  • 整合分析结果显示,干旱会显著降低土壤CO2排放,且土壤呼吸对干旱的敏感性略高于土壤异氧呼吸.主要机制:首先,干旱会加剧土壤微生物的水分限制,影响微生物活性,从而直接减少土壤碳排放[31];其次,干旱会破坏土壤团聚体,导致底物供应减少,从而间接减少土壤碳排放[32];最后,干旱还可以通过抑制植被的光合作用和降低土壤有机碳分解对温度的敏感性来间接地减少土壤碳排放[33].因此,尽管土壤呼吸组分对水分的敏感性不同[13],但由于干旱会降低微生物活性,导致土壤微生物CO2产生对水分变化的敏感性下降[28,30].本研究结果也表明,土壤活性碳库和微生物生物量碳库在干旱条件下降低,用于土壤异氧呼吸的碳底物含量减少(图1c).干旱引起土壤CO2排放与植被碳库的变化呈显著正相关关系(图4a),其中植被总生物量碳和地上生物量碳对干旱的敏感性无显著性差异(协方差分析,p=0.42),表明干旱减少土壤CO2排放主要是通过影响植被生长和根系分泌物来实现的[2].本研究发现陆地生态系统碳收支平衡的重要标志——净生态系统生产力(NEP)对干旱为显著的负响应(图1b),这与Wu等[2]的Meta分析结果一致,其原因是干旱引起旱地生态系统净初级生产力(NPP)的降低,而不是土壤微生物异氧呼吸的增强(图1a,b).

  • 分析结果表明,与常规降水量或灌溉量相比,干旱也会显著降低土壤N2O排放,这与Hartmann等[34]、Homyak等[17]和Wu等[35]的Meta分析结果一致,主要原因是干旱条件下,土壤通气性增强,不利于反硝化过程产生N2O[17].同时,反硝化细菌主要依赖于土壤活性碳源的输入为其提供能量来源,土壤活性碳源的减少会导致反硝化微生物的活性降低,导致土壤N2O的产生和排放减少[36],本研究也证实了上述结论(图1c).此外,土壤水分减少会改变氧化剂(例如NO-3-N)和还原剂(有机碳)的比例,导致反硝化过程中N2O/N2的产生比例发生变化[37].Homyak等[17]的研究表明,干旱虽会改善土壤的通气性,但由硝化过程产生的N2O并没有明显增加.其主要原因可能是土壤水分含量低不利于硝化微生物对底物的利用,本研究中土壤总氮库和铵态氮库在干旱条件下无显著变化的结果,也进一步验证了上述解释(图1d).本研究认为虽然土壤中N2O主要是通过硝化和反硝化过程产生,但相比于硝化过程,反硝化过程对土壤水分减少更加敏感.因此,干旱减少土壤N2O排放主要是通过增强土壤通气性进而抑制反硝化过程和降低底物的流动性和有效性来实现的.

  • 图4 土壤碳氮排放对干旱的响应变化与土壤和植被碳氮库对干旱的响应变化的相关性

  • Fig.4 Correlations between changes in responses of soil carbon and nitrogen emissions to drought and changes in responses of soil and plant pool to drought

  • 3.3 土壤碳氮排放对干旱响应的其他影响因子

  • 除土壤碳输入外,土壤理化性质在影响土壤CO2和N2O排放对干旱响应方面也具有十分重要的作用.土壤CO2排放对干旱的响应与土壤温度呈负相关关系(图3),表明干旱对CO2排放的抑制作用随土壤温度的增加呈增强的趋势,其主要原因可能是温度增加导致土壤水分含量下降,从而进一步减少土壤CO2排放[38].干旱条件下增加土壤有机碳含量可以促进土壤CO2排放(图3),这是因为微生物呼吸可利用的碳底物含量增加,有利于土壤向大气排放CO2[2].本研究发现土壤N2O排放对干旱的响应依赖于土壤可溶性有机碳的变化(图4c),造成这一现象的主要原因可能是土壤活性碳源的增加可以改善土壤碳氮比,提高土壤反硝化微生物活性,进而促进土壤N2O的产生和排放[39].干旱导致的土壤CO2排放变化与土壤微生物生物量碳氮库的变化呈显著正相关关系(图4b),且两者对干旱的敏感性无显著性差异,可能原因是随着土壤微生物生物量碳氮含量的增加,微生物可以利用的活性碳氮底物也随之增加,进而促进土壤CO2的排放[40].干旱引起的土壤N2O排放变化与土壤矿质氮含量的变化呈显著负相关关系(图4d),本研究推测这可能是因为土壤矿质氮含量的增加会影响土壤碳氮比,导致微生物产生的N2O进一步减少.

  • 除上述结论外,本研究还发现干旱对土壤CO2排放的影响与试验的持续时间呈显著正相关关系(表2),Yan等[18]也发现了同样的结论,造成这一现象的原因可能是微生物对干旱可能会产生一定的适应性,随着时间的推移,其对微生物的抑制效应将会有所缓和.

  • 3.4 研究展望

  • 本研究首次将干旱对土壤CO2和N2O排放的影响与植被和土壤碳氮库的变化联系起来,但仍存在以下不足:1)由于缺乏同步观测数据,本研究主要集中在研究干旱对旱地生态系统碳氮过程的影响,尚缺乏与其他气候变化因子(如大气CO2浓度升高、氮沉降)的交互效应;2)本研究包括的观测位点主要集中在全球温带和亚热带地区,尚缺少针对温室气体排放风险较高以及氮负荷较高的热带地区的研究报道[41];3)其他土壤养分(如氮、磷和钾)循环对干旱的响应以及多种养分协同影响土壤碳氮循环过程的相关机制还不清楚,也是目前以及今后全球变化领域需要解决的科学问题[42].

  • 4 结论

  • 基于整合分析表明,干旱会显著降低旱地生态系统土壤碳氮排放的特征和强度、植被的固碳效应以及土壤的活性碳库(可溶性有机碳),相反,土壤的活性氮库(硝态氮)在干旱条件下却显著增加.此外,干旱还会引起净生态系统生产力显著降低,导致在未来干旱的气候条件下,加剧旱地生态系统对气候变化的正反馈效应.本研究对全球试验数据的整合分析使我们能够概括过去单个研究关于旱地生态系统碳氮过程对干旱响应的相互矛盾的结果,进而为生物地球化学模型的发展提供理论基础,以科学预测陆地生态系统对气候变化的反馈效应.

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    • [17] Homyak P M,Allison S D,Huxman T E,et al.Effects of drought manipulation on soil nitrogen cycling:a meta-analysis[J].Journal of Geophysical Research:Biogeosciences,2017,122(12):3260-3272

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    • [19] Shi Z,Thomey M L,Mowll W,et al.Differential effects of extreme drought on production and respiration:synthesis and modeling analysis[J].Biogeosciences,2014,11(3):621-633

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    • [23] Ogaya R,Peñuelas J.Tree growth,mortality,and above-ground biomass accumulation in a holm oak forest under a five-year experimental field drought[J].Plant Ecology,2007,189(2):291-299

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    • [29] Schimel J P,Balser T C,Wallenstein M.Microbial stress-response physiology and its implications for ecosystem function[J].Ecology,2007,88(6):1386-1394

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    • [32] Smith A P,Bond-Lamberty B,Benscoter B W,et al.Shifts in pore connectivity from precipitation versus groundwater rewetting increases soil carbon loss after drought[J].Nature Communications,2017,8(1):1-11

    • [33] McCulley R L,Boutton T W,Archer S R.Soil respiration in a subtropical savanna parkland:response to water additions[J].Soil Science Society of America Journal,2007,71(3):820-828

    • [34] Hartmann A A,Niklaus P A.Effects of simulated drought and nitrogen fertilizer on plant productivity and nitrous oxide(N2O)emissions of two pastures[J].Plant and Soil,2012,361(1):411-426

    • [35] Wu D,Cárdenas L M,Calvet S,et al.The effect of nitrification inhibitor on N2O,NO and N2 emissions under different soil moisture levels in a permanent grassland soil[J].Soil Biology and Biochemistry,2017,113:153-160

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    • [38] Liu S W,Zheng Y J,Ma R Y,et al.Increased soil release of greenhouse gases shrinks terrestrial carbon uptake enhancement under warming[J].Global Change Biology,2020,26(8):4601-4613

    • [39] van Groenigen K J,Six J,Hungate B A,et al.Element interactions limit soil carbon storage[J].Proceedings of the National Academy of Sciences,2006,103(17):6571-6574

    • [40] Zheng Y J,Jin Y G,Ma R Y,et al.Drought shrinks terrestrial upland resilience to climate change[J].Global Ecology and Biogeography,2020,29(10):1840-1851

    • [41] Thornton P E,Lamarque J F,Rosenbloom N A,et al.Influence of carbon-nitrogen cycle coupling on land model response to CO2 fertilization and climate variability[J].Global Biogeochemical Cycles,2007,21(4):GB4018

    • [42] Galloway J N,Townsend A R,Erisman J W,et al.Transformation of the nitrogen cycle:recent trends,questions,and potential solutions[J].Science,2008,320(5878):889-892

  • 基本信息

    中图分类号: S153;X71
    文献标识码: A
    DOI: 10.13878/j.cnki.jnuist.2022.01.001

    基金信息

    国家自然科学基金(41771268,41225003,41771323)；

    引用信息

    稿件历史

    收稿日期: 2021-12-08

  • 参考文献

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